Known types of fluid-operated drilling tools, particularly “down-the-hole” rock drilling tools, generally have one end connected to a source of pressurized fluid (referred to here as the proximal end) and an opposite distal or working end with a reciprocating bit that is controlled to strike material to be drilled or removed with high force.
In a conventional rock drilling tool, the source of pressurized fluid, which is typically compressed air or other gas, is connected to a backhead or top sub at the proximal end of the tool by a pressure fitting. A hollow wear sleeve is attached by a threaded connection to the backhead and extends distally to form the exterior surface or shank of the tool. Within the wear sleeve, there is a distributor with a check valve that selectively supplies pressurized fluid to move the piston.
Typically, the distributor is secured in place by its attachment to an interior surface of the wear sleeve. According to one known approach, the distributor is received within the bore of an inner cylinder, and the inner cylinder has a surrounding retaining ring that is received in a circumferential groove formed in the interior surface of the wear sleeve. Over time, it becomes necessary to remove the distributor, e.g., to repair or replace it, to replace the wear sleeve to which it is attached and/or to access other components within the wear sleeve, e.g., the piston. In conventional drilling tools, uncoupling the distributor from the wear sleeve is difficult. For example, it can be difficult to access the retaining ring and disengage it from the wear sleeve and/or the distributor.
In conventional drilling tools, some of the passageways for the pressurized fluid have reduced areas and/or other types of restrictions that decrease flow velocity and efficiency. Some of the passageways extend between coaxially positioned components, and some are formed at least in part by channels, grooves, openings, etc., formed in walls of the components.
In the operation of some drilling tools, such as a down-the-hole rock drilling tool, the tool is designed such that when the bit encounters a very low resistance during operation, such as when the bit encounters a void in the material being drilled, the bit is extended to a “drop open” position and further movement of the bits is stopped. In the way, the possibility for damage to the tool or to the operation is minimized. It would be advantageous to decrease the transition time for changing from a normal operating position to the drop open position.
In addition, the speed at which the tool transitions between other phases of operation is affected by the piston area. It would be advantageous to reduce the transition times between other phases of operation to improve overall efficiency.